Area Forecast Discussion
Issued by NWS Portland, OR

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568
FXUS66 KPQR 230359
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
859 PM PDT Sat Jul 22 2017

.SYNOPSIS...A weak upper trough will pass over Washington on Sunday
for a slight increase in onshore flow over southwest Washington and
northwest Oregon, bringing a bit of cooling to to the coast and to
the northern Willamette Valley. An upper ridge will build over our
forecast area on Monday and Tuesday for a warming trend. An upper
level low to our southwest may produce some thunderstorms in the Lane
County Cascades Sunday through Tuesday afternoon and evening.
Increased onshore flow and cooler conditions are expected for the
second half of next week, bringing temperatures back to near normal.
&&

.SHORT TERM...Tonight through Tuesday...A fair amount of low clouds
were solidifying along the Washington and Oregon coasts this evening
and will spread inland later tonight and Sunday morning as an upper
trough passing by to the north on Sunday results in increased onshore
flow. While Saturday afternoon temperatures reached the lower 90s in
most valley locations, we should see about 5 degrees o cooling
Sunday, especially north.

There is a developing upper low off the coast of California which
will move to near the northern California coast Sunday and linger
through at least Tuesday. Southerly flow develops aloft ahead of the
low and will likely result in increasing higher level moisture and
instability over the southern portion of our Oregon Cascades for a
chance of thunderstorms Sunday afternoon through Tuesday, especially
during heating in the afternoon and evening hours. This appears to be
the most significant chance of lightning with the potential for fire
starts in the Cascades so far this summer. Models show that any
moisture that does form will be high level and not likely to produce
any significant precipitation from these storms. The southerly flow
combines with the upper ridge to the north of the low for warming on
both Monday and Tuesday, with highs in the valley in the lower 90s on
Monday and upper 80s on Tuesday. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
Tuesday night through Saturday...Models are in good agreement kicking
out the upper low over northern California and moving it northwest
during the day on Wednesday. Weak westerly flow develops at 700mb as
the low moves out it looks like the threat of thunderstorms will be
greatly reduced. However, this could change if the upper low lingers,
which they are notorious for doing this time of year. That could
prolong convection for another afternoon and evening heating cycle.

Models show a upper trough approaching from the northwest by Thursday
which puts us back in WSW flow aloft and drys out the Cascades ending
any thunderstorm threat. Night and morning low clouds may become more
extensive Thursday through Saturday with temperatures returning to
near normal. Schneider
&&

.AVIATION...Low clouds have moved onto the coast south of Tillamook,
with LIFR conditions expected to continue at ONP overnight tonight.
Clouds will eventually make their way up to KAST but expect cigs to
be a bit higher with IFR cigs later tonight. Inland is VFR tonight,
and will stay predominantly VFR overnight. Some indication in the
models that we will see some areas of MVFR cigs move into the north
Willamette Valley Sunday morning, but not feeling that confident
since there isn`t the solid cloud bank off the coast of AST just yet.
If MFR cigs do develop inland, expect them to clear by 17Z-18Z. Along
the coast, cigs will hold on until around 18Z-21Z. As winds increase
along the coast, expect improving conditions at ONP earlier than AST.
Expect a breezy day along the coast with wind gusts up to 30 kt
Sunday afternoon. Inland will become breezy as well with north winds
up to 20 kt.

KPDX AND APPROACHES...Predominantly VFR through the next 24 hours.
Small chance of MVFR cigs around 2000 ft moving into the terminal
between 13-17Z Sunday, but confidence is low. Gusty northwesterly
winds to 20 to 25 kt possible Sunday afternoon and evening. -McCoy
&&

.MARINE...No changes. Previous discussion follows...
High pressure will continue to strengthen over the NE Pacific this
afternoon, while hot weather over SW Oregon and NW California will
help to strengthen a thermal trough over those areas. This will bring
an increase in northerly winds, with gusts 25-30 kt expected across
our southern waters by sunset and spreading north into our northern
waters later tonight. The increasing winds will result in steep wind-
driven seas. Winds will continue to increase on Sunday. Models
continue to suggest that gale force winds are possible over our
southern waters. However, northerly gales over our waters are
relatively rare, so given that the stronger models continue to only
show marginal gales will stick with our current Small Craft
Advisories for winds and hazardous seas, but would not be surprised
local gusts to 35 kt. SCA conditions look to persist into Tuesday so
the current advisories will likely need to be extended. Models then
show an upper trough from the Gulf of Alaska moving closer to our
waters which will likely bring a decrease in winds/seas towards the
middle of next week. /64
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 6 AM PDT Monday for Coastal Waters
     from Cape Shoalwater WA to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to
     7 AM PDT Sunday.

&&

$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.



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